In the summer of 2012, a team of six climbers set out to attempt the first ascent of one of the great unclimbed lines of the Himalaya – the giant Mazeno Ridge on Nanga Parbat, the world’s ninth highest mountain. At ten kilometres in length, the Mazeno is the longest route to the summit of an 8,000-metre peak. Ten expeditions had tried and failed to climb this enormous ridge. Eleven days later two of the team, Sandy Allan and Rick Allen, both in their late fifties, reached the summit. They had...